Cellulosic and lignocellulosic feedstocks and wastes, such as agricultural residues, wood, forestry wastes, sludge from paper manufacture, and municipal and industrial solid wastes, provide a potentially large renewable feedstock for the production of valuable products such as fuels and other chemicals. Cellulosic and lignocellulosic feedstocks and wastes, composed of carbohydrate polymers comprising cellulose, hemicellulose, glucans and lignin are generally treated by a variety of chemical, mechanical and enzymatic means to release primarily hexose and pentose sugars, which can then be fermented to useful products.
First, biomass feedstocks are treated to make the carbohydrate polymers of cellulosic and lignocellulosic materials more readily available to saccharification enzymes, which is often called pretreatment. The pretreated biomass is then further hydrolyzed in the presence of saccharification enzymes to release oligosaccharides and/or monosaccharides in a hydrolysate. Saccharification enzymes used to produce fermentable sugars from pretreated biomass typically include one or more glycosidases, such as cellulose-hydrolyzing glycosidases, hemicellulose-hydrolyzing glycosidases, and starch-hydrolyzing glycosidases, as well as peptidases, lipases, ligninases and/or feruloyl esterases. Saccharification enzymes and methods for biomass treatment are reviewed in Lynd, L. R., et al. (Microbiol. Mol. Biol. Rev. (2002) 66:506-577).
It is desirable to have a system and/or method for treating biomass that is effective and economical for use on a large scale. Treatment of biomass as a concentrated, high dry weight material is needed to produce the high concentrations of fermentable sugars needed for fermentation to products economically. Thus movement of material including a high dry weight fraction of biomass through a reactor while maintaining the ability of treatment chemicals to penetrate and optimally prepare the biomass for saccharification, in addition to using minimal chemical and energy inputs, is a challenge for biomass treatment processes. Also a method that includes low capital cost equipment is desired. Methods including reactors with no requirement for stirring or reactor rotation may provide lower capital cost for equipment and lower energy input.
Systems not requiring stirring or reactor rotation and specifying means for moving biomass through a reactor have been described. U.S. Pat. No. 4,186,658 discloses an apparatus for conveying particulate material, such as wood chips, straw, bagasse and other fibrous material, which compacts the material into a solid “plug” state. A screw conveyor pre-compacts the material, with further compaction by a reciprocating piston. The compact plug is so dense that it is capable of effectively preventing blow-back within the system. The plug may then be fed to a means for processing the material. A dense plug of biomass material would not be optimally accessible by pretreatment reactants.
Similarly, U.S. Pat. No. 4,136,207 discloses a process for preparing cellulosic material with enhanced digestibility by ruminants that begins with mechanically compacting the material. It is then subjected to high steam pressure in the absence of chemical reagents, and is further compacted to form a solid plug of biomass which prevents escape of steam through the inlet. Small portions of the material are then discharged, subjecting it to rapid reduction in pressure. The compacting of biomass into a plug would not allow optimal accessibility by chemical reagents used in pretreatment.
U.S. Pat. No. 6,176,176 discloses an apparatus for treating cellulosic materials that uses a rotatable screw mounted in a barrel of an extruder. Liquid ammonia under pressure is fed into the barrel and mixed with lignocellulosic material in the barrel, then the lignocellulosic material containing the ammonia is expanded explosively by change of liquid ammonia to a gas as it exits the barrel through a heated die. Use of an extruder in a large scale commercial process would be very costly and therefore not provide an economical process.
A method for treating biomass to produce fermentable sugars which uses low strength aqueous ammonia to pretreat high concentration biomass is disclosed in co-owned and co-pending U.S. Ser. No. 11/402,757.
There remains a need for a system and/or method for treating biomass that moves high dry weight of biomass through a low-cost reactor while allowing for maximal accessibility by chemical reactants, to prepare the biomass for saccharification.